At present, most smartphones each have a camera built therein. The performance of the camera built into a smartphone has been improved and is now comparable to the performance of a digital still camera (DSC) and a digital single lens reflex camera (DSLR camera). To further expand the range of the application of the camera built into a smartphone, a high-quality zoom function has been increasingly required.
In general, the camera built into a smartphone uses a fixed focal lens instead of a zoom lens due to restriction on the size and thickness. The zoom function is achieved as follows:
1. Electronic Signal Processing
Part of an entire captured image is cropped and electronically enlarged and further caused to undergo sharpness control, super-resolution processing, and other types of detail/resolution enhancement.
2. Use of Two Cameras
Two cameras, a wide-angle camera and a telephoto camera, are used. Two images from the two cameras are combined with each other in accordance with the zoom position.
A problem with the method described in the above item 1 is a decrease in resolution because an image is cropped. For example, when an image sensor having a total pixel number of 8 M is used to capture an image of 2× zoom magnification, the number of pixels of the enlarged image undesirably decreases to 2 M. The decrease in the number of pixels lowers the resolution and therefore loses information on details and texture. Even when sharpness control and super-resolution processing are performed, it cannot be said that a lossless zoom function is achieved, and image quality of details is inferior to that achieved by optical zooming.
The method described in the above item 2 has a problem of design (exterior appearance) of the smartphone because a telephoto lens has a long focal length. When a telephoto lens is built into a thin smartphone, the portion where the telephoto lens is built in is thicker than the other portion, resulting in deterioration in exterior appearance.